Resolver

ABSTRACT

Disclosed is a resolver robust against external noise and having a reduced error in the detection of a rotation angle, which includes a stator made of a magnetic material and having a plurality of teeth and a plurality of slots alternately formed at an inner side thereof, insulation covers respectively having a tooth insulating unit formed at an inner side thereof corresponding to the teeth and mounted to the stator at both upper and lower surfaces of the stator, and coils wound on the teeth with the tooth insulating unit being interposed therebetween, wherein regarding winding widths of coils located at an outermost circumference among the wound coils, a ratio of a shortest winding width to a longest winding width is 0.69 or above and 1 or below.

TECHNICAL FIELD

The present application claims priority to Korean Patent Application No. 10-2015-0159831 filed on Nov. 13, 2015 in the Republic of Korea, the disclosures of which are incorporated herein by reference.

The present disclosure relates to a device for detecting a rotation angle of a rotating device, and more particularly, to a resolver.

BACKGROUND

When controlling a rotating device, for example a motor, rotation information should be detected precisely and rapidly. When controlling a rotating device, a movement or rotating location of a rotating body should be measured accurately by means of a rotation angle detecting device installed at a rotary shaft. A resolver and an encoder have been adopted and used for such measurement, and these detecting devices have advantages and disadvantages. The resolver directly detects an absolute location of a rotor and calculates a rotating direction and a rotating speed by means of the change of location of the rotor.

An electric power steering (EPS) is used for a vehicle in order to assist the operation of a handle by driving a motor with a battery. The electric power steering receives attention as an efficient system with a less power loss of an engine, in comparison to a case where a hydraulic pressure is generated by means of a rotating force of an engine. Since the EPS needs precise control, a rotation angle detecting device for precisely detecting a rotation angle of the motor is required, and the rotation angle detecting device demands high reliability. As such a rotation angle detecting device for a vehicle, a resolver having higher environment resistance in comparison to an encoder is used.

The resolver is a kind of sensor for precisely measuring a rotating speed and a rotation angle of a motor. Generally, the resolver has a relatively simple structure in which both an excitation coil and an output coil are located at a stator and an oval or multi-pole rotor is located at an inner side of the stator. A resolver having this structure is disclosed in Japanese Unexamined Patent Publication No. 1996-178610.

FIG. 1 is a diagram in the above Japanese Unexamined Patent Publication, and a resolver includes a rotor 10 having a rotary shaft provided therethrough and a ring-shaped stator 11 configured to face the rotor 10 with a gap. The rotor 10 has a plurality of salient poles 10 a formed along an outer circumference thereof, and the ring-shaped stator 11 has a plurality of teeth 11 b and a plurality of slots 11 a alternately formed along an inner circumference thereof. In addition, an excitation coil and an output coil are wound on the teeth 11 b of the stator 11, and the excitation coil and the output coil are accommodated in the slots 11 a. Here, the output coil is composed of a first output coil and a second output coil. If an excitation power is applied to the excitation coil and the rotary shaft is rotated, a sine signal and a cosine signal are output from the first output coil and the second output coil, and a rotation angle of the resolver may be known by analyzing the signals.

As described above, in the resolver, the coils wound on the teeth 11 b of the stator 11 is an important element for inputting and outputting signals, and thus a precise design is demanded when winding the coils at a rotation angle detecting device such as a resolver. For example, when the coil is wound, if the coil is would irregularly, a high-frequency wave may be generated at an outer waveform, or electric interference may be caused between coils wound on two adjacent teeth 11 b, thereby generating an error in detecting a rotation angle. In addition, if a coil is wound more on the teeth 11 b, an area occupied by the coil at the slot 11 a between the teeth 11 b increases, which causes electric interference between coils wound on two adjacent teeth 11 b and results in an error. If a coil is wound less on the teeth 11 b, a transformation ratio of an induced voltage of the output coil is lowered, which becomes vulnerable to external noise.

Patent Literature: Japanese Unexamined Patent Publication No. 1996-178610

DISCLOSURE Technical Problem

The present disclosure is designed according such a technical demand, and therefore the present disclosure is directed to providing a resolver which is robust against external noise and has a reduced error in the detection of a rotation angle.

Technical Solution

In one aspect of the present disclosure, there is provided a resolver, comprising: a stator made of a magnetic material and having a plurality of teeth and a plurality of slots alternately formed at an inner side thereof; insulation covers respectively having a tooth insulating unit formed at an inner side thereof corresponding to the teeth and mounted to the stator at both upper and lower surfaces of the stator; and coils wound on the teeth with the tooth insulating unit being interposed therebetween, wherein regarding winding widths of coils located at an outermost circumference among the wound coils, a ratio of a shortest winding width to a longest winding width is 0.69 or above and 1 or below.

The ratio of the shortest winding width to the longest winding width among the wound coils may be 0.8 or above and 1 or below.

A coil occupying ratio per slot, which is defined by the following equation and represents a ratio of area occupied by the coils in a slot to which the insulation covers are fixed, may be 35% or below:

Equation

Coil occupying ratio per slot=(area occupied by coils in a single slot)/(area of a single slot).

The coil occupying ratio per slot may be 3% or above.

In a slot to which the insulation covers are fixed, a shortest distance between coils wound on two teeth adjacent to each other may be 4 mm or above.

The resolver may further comprise a rotor made of a magnetic material and configured to rotate based on a rotary shaft to change a gap permeance together with the stator.

The rotor may be an inner-type rotor disposed at an inner center of the stator.

The rotor and the stator may be formed by laminating a plurality of magnetic steel plates with a predetermined thickness.

The stator may be formed by manufacturing the magnetic steel plates into a ring shape having a plurality of teeth and a plurality of slots alternately formed at an inner side thereof and then laminating the magnetic steel plates.

The rotor may be ring-shaped having a through hole formed at a center portion thereof so that the rotary shaft is inserted therein and a plurality of salient poles formed at an outer circumference thereof to change the gap permeance.

The salient pole may have an arc shape with a diameter smaller than at least a diameter of the rotor.

A center of the arc may be disposed spaced apart from a center of the rotor by a predetermined distance, and the arcs of the plurality of salient poles have the same diameter.

In another aspect of the present disclosure, there is also provided a resolver, comprising: a stator made of a magnetic material and having a plurality of teeth and a plurality of slots alternately formed at an inner side thereof; insulation covers respectively having a tooth insulating unit formed at an inner side thereof corresponding to the teeth and mounted to the stator at both upper and lower surfaces of the stator; and coils wound on the teeth with the tooth insulating unit being interposed therebetween, wherein regarding winding widths of coils located at an outermost circumference among the wound coils, a ratio of a mean winding width of the coils located at the outermost circumference to a longest winding width is 0.83 or above and 1 or below, and wherein regarding the winding widths of the coils located at the outermost circumference among the wound coils, a ratio of the mean winding width of the coils located at the outermost circumference to a shortest winding width is 1 or above and 1.16 or below.

Regarding the winding widths of the coils located at the outermost circumference among the wound coils, a ratio of the shortest winding width to the longest winding width may be 0.69 or above and 1 or below.

Regarding the winding widths of the coils located at the outermost circumference among the wound coils, a ratio of the mean winding width of the coils located at the outermost circumference to the longest winding width may be 0.89 or above and 1 or below, and regarding the winding widths of the coils located at the outermost circumference among the wound coils, a ratio of the mean winding width of the coils located at the outermost circumference to the shortest winding width may be 1 or above and 1.1 or below.

Regarding the winding widths of the coils located at the outermost circumference among the wound coils, a ratio of the shortest winding width to the longest winding width may be 0.8 or above and 1 or below.

A coil occupying ratio per slot, which is defined by the following equation and represents a ratio of area occupied by the coils in a slot to which the insulation covers are fixed, may be 35% or below:

Equation

Coil occupying ratio per slot=(area occupied by coils in a single slot)/(area of a single slot).

The coil occupying ratio per slot may be 3% or above.

In a slot to which the insulation covers are fixed, a shortest distance between coils wound on two teeth adjacent to each other may be 4 mm or above.

The resolver may further comprise a rotor made of a magnetic material and configured to rotate based on a rotary shaft to change a gap permeance together with the stator.

The rotor may be an inner-type rotor disposed at an inner center of the stator.

The rotor and the stator may be formed by laminating a plurality of magnetic steel plates with a predetermined thickness.

The stator may be formed by manufacturing the magnetic steel plates into a ring shape having a plurality of teeth and a plurality of slots alternately formed at an inner side thereof and then laminating the magnetic steel plates.

The rotor may be ring-shaped having a through hole formed at a center portion thereof so that the rotary shaft is inserted therein and a plurality of salient poles formed at an outer circumference thereof to change the gap permeance.

The salient pole may have an arc shape with a diameter smaller than at least a diameter of the rotor.

A center of the arc may be disposed spaced apart from a center of the rotor by a predetermined distance, and the arcs of the plurality of salient poles have the same diameter.

Advantageous Effects

The resolver of the present disclosure may precisely measures a rotation angle of a rotating device such as a motor since the resolver is robust against external noise and has an output waveform of enhanced accuracy.

The resolver of the present disclosure may have improved product performance by reducing interference between magnetic fluxes generated at adjacent teeth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a resolver in the related art.

FIG. 2 is a perspective view showing a resolver according to an embodiment of the present disclosure.

FIG. 3 is a partial plane view showing the resolver of FIG. 2.

FIG. 4 is a diagram showing a rotor of the resolver according to an embodiment of the present disclosure.

FIG. 5 is a partial horizontal sectional view showing a resolver according to an embodiment of the present disclosure, which depicts a wound shape of a coil.

FIG. 6 is a partial horizontal sectional view showing a resolver according to an embodiment of the present disclosure, for illustrating a winding width.

FIG. 7 is a diagram showing a test environment of the resolver according to an embodiment of the present disclosure.

FIG. 8 is a graph showing a maximum error rate of each sample resolver according to a l_(min)/l_(max) ratio.

FIG. 9 is a graph showing a maximum error rate of each sample resolver according to a l_(mean)/l_(max) ratio.

FIG. 10 is a graph showing a maximum error rate of each sample resolver according to a l_(mean)/l_(min) ratio.

FIG. 11 is an enlarged view showing a portion A of FIG. 3.

FIG. 12 is a diagram for illustrating a shortest distance between coils according to an embodiment of the present disclosure.

FIGS. 13, 14, 15, 16, 17, 18, 19, 20 and 21 are graphs showing an error rate of each resolver prepared as a sample.

BEST MODE

The above objects, features and advantages of the present disclosure will become apparent from the following descriptions of the embodiments with reference to the accompanying drawings, from which it will be deemed that a person having ordinary skill can easily practice the technical features of the present disclosure. Also, any explanation of the prior art known to relate to the present disclosure may be omitted if it is regarded to render the subject matter of the present disclosure vague. Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

FIG. 2 is a perspective view showing a resolver according to an embodiment of the present disclosure, FIG. 3 is a partial plane view showing the resolver of FIG. 2, and FIG. 4 is a diagram showing a rotor of the resolver according to an embodiment of the present disclosure.

Referring to FIGS. 2, 3 and 4, a resolver of this embodiment includes a rotor 300, a stator 110 made of a magnetic material and having a plurality of teeth 111 and a plurality of slots 112 alternately formed along an inner circumference thereof, ring-shaped insulation covers 120 mounted to both upper and lower surfaces of the stator 110, and coils 140 respectively wound on the teeth 111 with the insulation cover 120 being interposed therebetween.

The rotor 300 is a ring-shaped ferromagnetic body having a through hole 301 formed at center portion thereof so that a rotary shaft is inserted through the through hole 301. The rotor 300 may be formed by laminating magnetic steel plates of a predetermined thickness. The rotor 300 serves as an inner-type ferromagnetic body disposed at an inner center of the stator 110 and has a plurality of salient poles formed along an outer circumference thereof to transform a gap permeance together with the stator 110 while rotating based on the rotary shaft. At this time, the salient pole of the rotor 300 has an arc shape having a diameter R2 smaller than a diameter R1 of the rotor 300. A center C2 of the arc of the salient pole is disposed spaced apart from a center C1 of the rotor 300 by a predetermined distance, and the diameter R2 of the arc of each salient pole may be identical to each other.

The stator 110 is a ring-shaped ferromagnetic body having a plurality of teeth 111 formed along an inner circumference thereof to face the rotor 300 with a gap and slots 112 between adjacent teeth 111. The stator 110 may be prepared by manufacturing magnetic steel plates into a ring shape having a plurality of teeth 111 and a plurality of slots 112 alternately formed at an inner side thereof and laminating the magnetic steel plates.

The insulation covers 120 are mounted to both upper and lower surfaces of the stator 110 and are composed of an upper insulation cover and a lower insulation cover. The insulation cover 120 has a plurality of tooth insulating units 121 formed to cover the teeth 111 of the stator 110 at regular intervals along an inner circumference thereof. Since the insulation covers 120 are mounted to both upper and lower surfaces of the stator 110, the tooth insulating units 121 cover the upper and lower surfaces of the teeth 111.

In a state where the insulation covers 120 are mounted and fixed to both upper and lower surfaces of the stator 110, the coils 140 are wound on the tooth insulating units 121. In other words, the coil 140 is wound on the teeth 111 with the tooth insulating unit 121 being interposed therebetween, without directly contacting the teeth 111. Since the coil 140 is wound on the teeth 111 with the tooth insulating unit 121 being interposed therebetween, the coil 140 is accommodated in the slot 112. The coil may be composed of a one-phase excitation coil and two-phase output coils. One output coil of the two-phase output coils outputs a SIN signal, and the other output coil outputs a COS signal. If an excitation voltage is applied to the excitation coil and the rotary shaft is rotated, the first output coil and the second output coil outputs a sine signal and a cosine signal, and a rotation angle of the resolver may be known by analyzing the signals.

In the resolver, when a coil is wound on the teeth 111 by means of the tooth insulating unit 121, the coil may be wound in various shapes. FIG. 5 is a partial horizontal sectional view showing a resolver according to an embodiment of the present disclosure, which depicts a wound shape of a coil. Here, (a) of FIG. 5 depicts that the coils accommodated in the slot 112 has a trapezoidal shape in the slot 112, (b) of FIG. 5 shows that the coils accommodated in the slot 112 has a rectangular shape in the slot 112. In addition, coils may be wound on the teeth 111 in various shapes.

In the resolver as described above, the coils should be wound uniformly on the teeth 111 by means of the tooth insulating unit 121. If the coils are wound irregularly, a high-frequency wave may be generated at an outer waveform, or electric interference may be caused between coils wound on two adjacent teeth 111, thereby generating an error in detecting a rotation angle. Parameters for evaluating uniformity of wound coils may be defined as follows.

FIG. 6 is a partial horizontal sectional view showing a resolver according to an embodiment of the present disclosure, for illustrating a winding width. In FIG. 6, a coil at an outermost circumference is depicted among the coils wound on the teeth 111 by means of the tooth insulating unit 121. (a) of FIG. 6 depicts a case where coils are wound in a rectangular shape, (b) FIG. 6 depicts a case where coils are wound in a trapezoidal shape, and (c) of FIG. 6 depicts a case where coils are wound with a convex center.

Referring to FIG. 6, coils wound on the teeth 111 at an outermost circumference respectively have winding widths of l₁, l₂ . . . l_(n), in a radial direction. At this time, the winding width means a length of a coil which extends out vertically from the slot 112, cross the tooth insulating unit 121 and come into an adjacent slot 112 vertically. Based on a section of a coil, a start point and an end point of the coil may be set from a center of the coil or from an outer circumference of the coil. In this embodiment, the start point and the end point of the coil are set based on the center of the coil. From the winding widths of the coils, three parameters are defined. In other words, (1) a l_(mean)/l_(max) ratio, (2) a l_(mean)/l_(min) ratio, and (3) a l_(min)/l_(max) ratio are defined. l_(mean) represents a mean of winding widths (l₁, l₂ . . . l_(n)) of coils, l_(max) represents a longest winding width among winding widths (l₁, l₂ . . . l_(n)) of coils, and l_(min) represents a shortest winding width among winding widths (l₁, l₂ . . . l_(n)) of coils.

The l_(min)/l_(max) ratio is a ratio between a shortest winding width and a longest winding width. If the l_(min)/l_(max) ratio is 1, this means that all winding widths are equal to each other and thus coils are wound uniformly. If the l_(min)/l_(max) ratio is smaller than 1, this means that coils are wound more irregularly. The l_(mean)/l_(max) ratio is a ratio between a mean of the winding widths and a longest winding width, and the l_(mean)/l_(min) ratio is a ratio between a mean of the winding widths and a shortest winding width. If both the l_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratio are 1, this means that all winding widths are equal to each other and thus coils are wound uniformly. If the l_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratio are smaller than 1, this means that coils are wound more irregularly. Therefore, the uniformity of wound coils of the resolver may be evaluated by using the l_(min)/l_(max) ratio, or by using the l_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratio.

Generally, the resolver is demanded to have an error rate of 0.5 or below. First, when the l_(min)/l_(max) ratio is used as a basis, if the l_(min)/l_(max) ratio is 0.69 or above and 1 or below, the error rate becomes 0.5 or below. Next, when the l_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratio are used as a basis, if the l_(mean)/l_(max) ratio is 0.83 or above and 1 or below and the l_(mean)/l_(min) ratio is 1 or above and 1.16 or below, the error rate becomes 0.5 or below. Preferably, when the l_(min)/l_(max) ratio is used as a basis, it is desirable that the l_(min)/l_(max) ratio is 0.8 or above and 1 or below. If the l_(min)/l_(max) ratio is lower than 0.8, the error rate increases abruptly in comparison to a case where the l_(min)/l_(max) ratio is 0.8 or above. Therefore, in order to operate the resolver stably, it is most desirable that the l_(min)/l_(max) ratio is 0.8 or above and 1 or below. When the l_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratio are used as a basis, it is most desirable that the l_(mean)/l_(max) ratio is 0.89 or above and 1 or below, and the l_(mean)/l_(min) ratio is 1 or above and 1.1 or below.

Hereinafter, results of the performance test of a resolver according to the uniformity of wounded coils will be described with reference to Table 1 below.

Preparation of Samples

A stator 110 having twenty-four slots 112, insulation covers 120, a rotor 300 having eight salient poles and coils 140 are prepared. At this time, the stator 110 and the rotor 300 are ferromagnetic bodies with high magnetic permeability and are manufactured by laminating steel plates with a thickness of 0.5 mm in order to reduce a core loss. After the stator 110 and the insulation cover 120 are assembled, an excitation coil and an output coil are wound on each slot 112 by means of a circular winding machine to fabricate a resolver. 14 resolvers were prepared by designating a coil diameter of 0.15 mm a winding pitch of 0.1555 mm and changing a winding shape of the coils variously. If the coils have a trapezoidal winding shape, when a first coil is wound, a winding start point and a winding end point are set to a start point and an end point of the slot 112, and the winding start point is changed from a second coil, while the winding end point is maintained identically. If the coils have a convex winding shape, when a first coil is wound, a winding start point and a winding end point are set to a start point and an end point of the slot 112, and the winding start point and the winding end point are changed from a second coil.

Measurement of an Error Rate

FIG. 7 is a diagram showing a test environment of the resolver according to an embodiment of the present disclosure. After each resolver is prepared as described above in relation to sample preparation, each resolver 630 is coupled to one end of a rotary shaft of a motor 610, and an encoder 620 is coupled to the other end of the rotary shaft. In addition, a calculator 640 analyzes output waveforms of the resolver 630 and the encoder 620. In detail, after the rotary shaft of the motor 610 is operated, the calculator 640 calculates a rotation angle profile by analyzing the output waveform of the resolver 630 and calculates an error rate by comparing the rotation angle profile with a rotation angle profile of the encoder 620. Each resolver 630 is tested ten times, among which a greatest error rate is defined as a maximum error rate. Generally, the resolver is demanded to have a maximum error rate of 0.5 or below. The winding width of the coil is checked by means of x-ray inspection.

TABLE 1 maximum l_(mean)/_(lmax) l_(mean)/l_(min) l_(min)/l_(max) error rate Example 1 0.993 1.005 0.982 0.258 Example 2 0.975 1.023 0.954 0.263 Example 3 0.952 1.049 0.916 0.265 Example 4 0.937 1.061 0.886 0.272 Example 5 0.929 1.07 0.851 0.275 Example 6 0.91 1.089 0.825 0.288 Example 7 0.892 1.099 0.803 0.298 Example 8 0.875 1.109 0.759 0.352 Example 9 0.858 1.149 0.72 0.412 Example 10 0.841 1.152 0.698 0.475 Comparative Example 1 0.824 1.178 0.649 0.525 Comparative Example 2 0.802 1.195 0.612 0.567 Comparative Example 3 0.795 1.207 0.588 0.602 Comparative Example 4 0.773 1.229 0.543 0.627

FIG. 8 is a graph showing a maximum error rate of each sample resolver according to l_(min)/l_(max) ratio, FIG. 9 is a graph showing a maximum error rate of each sample resolver according to l_(mean)/l_(max) ratio, and FIG. 10 is a graph showing a maximum error rate of each sample resolver according to l_(mean)/l_(min) ratio. In other words, FIGS. 8, 9 and 10 express Table 1 with graphs.

Referring to Examples 1 to 10 of Table 1 and FIG. 8, when the l_(min)/l_(max) ratio is used as a basis, if the l_(min)/l_(max) ratio is 0.69 or above and 1 or below, the maximum error rate is 0.5 or below. Next, Referring to Table 1 and FIGS. 9 and 10, when the l_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratio are used as a basis, if the l_(mean)/l_(max) ratio is 0.83 or above and 1 or below and the l_(mean)/l_(min) ratio is 1 or above and 1.16 or below, the maximum error rate is 0.5 or below. Meanwhile, seeing Comparative Examples 1 to 4, if the above ratio condition is not satisfied, the maximum error rate is greater than 0.5.

Meanwhile, in Examples 1 to 7, the error rate increases as much as 0.0057 on average, but in Examples 8 to 10, the error rate increases as much as 0.03075 on average. This is because, when the l_(min)/l_(max) ratio is smaller than 0.8, the error rate increases more greatly in comparison to a case where the l_(min)/l_(max) ratio is 0.8 or above. Therefore, in order to operate the resolver stably, it is most desirable that the l_(min)/l_(max) ratio is 0.8 or above and 1 or below. In addition, when the l_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratio are used as a basis, it is most desirable that the l_(mean)/l_(max) ratio is 0.89 or above and 1 or below, and the l_(mean)/l_(min) ratio is 1 or above and 1.1 or below.

Meanwhile, in this resolver, when the coil is wound on the teeth 111 with the tooth insulating unit 121 being interposed therebetween and accommodated in the slot 112 in a state where the insulation cover 120 is fixed, a coil occupying ratio per slot, which represents a ratio of area occupied by coils in an area of a single slot 112, gives a serious influence on the performance of the resolver. The coil occupying ratio per slot may be expressed as in Equation 1 below.

Coil occupying ratio per slot=(area occupied by coils in a single slot)/(area of a single slot)  Equation 1

The occupying ratio will be described below in more detail. FIG. 11 is an enlarged view showing a portion A of FIG. 3.

As described above, the plurality of teeth 111 and the plurality of slots 112 are alternately formed along the inner circumference of the stator 110. In addition, the insulation covers 120 are mounted and fixed to both upper and lower surfaces of the stator 110. The tooth insulating units 121 corresponding to the teeth 111 of the stator 110 are formed at the inner circumference of the insulation cover 120 to cover each tooth 11 of the stator 110 at both upper and lower surfaces thereof. At this time, when being observed on a plane, the tooth insulating unit 121 covering the teeth 111 is slightly greater than the teeth 111.

In other words, as shown in FIG. 11, the tooth insulating unit 121 may have a width margin (a) so that its width is slightly greater than the width of the teeth 111. Therefore, in this embodiment and the appended claims, the area of the slot 112 may be understood as an area from which an area of the width margin is excluded. In other words, in this embodiment, an area of a single slot 112 is not an area between two adjacent teeth 111 but an area between two adjacent tooth insulating units 121. In addition, an area of a single slot 111 is an area of a figure whose vertices correspond to four points (a, b, c, d) of two adjacent tooth insulating units 121 as depicted in FIG. 11.

In the area of the slot 112, an area occupied by the coils 140 may be obtained with the number of turns of the coils 140 and a diameter of each coil 140. For example, if the excitation coil turns by an n number and the output coil turns by a m number at each of two adjacent tooth insulating units 121 (it is assumed that the first output coil and the second output coil have the same radius), an area of the coils 140 accommodated in the slot 112 between the two tooth insulating units 121 may be obtained as in Equation 2 below.

Area of coil=2nπr ₁ ²+4mπr ₂ ²  Equation 2

Here, r₁ represents a radius of the excitation coil, and r₂ represents a radius of the output coil.

Generally, a minimum number of turns of the output coil required when the excitation coil is wound on the tooth insulating unit 121 may be obtained as in Equation 3 below. In Equation 3, a represents the number of turns of the excitation coil, b represents a transformation ratio, c represents a minimum air gap between the stator and the rotor, d represents a sectional area of each coil, and e represents an input voltage.

$\begin{matrix} {{{Minimum}\mspace{14mu} {number}\mspace{14mu} {of}\mspace{14mu} {turns}\mspace{14mu} {of}\mspace{14mu} {output}\mspace{14mu} {oil}} = {\frac{a}{1 - b} \times c \times b \times e \times \frac{1}{d \times 100}}} & {{Equation}\mspace{14mu} 3} \end{matrix}$

Generally, the input voltage input to the excitation coil is at least 4 Vrms and has a frequency of 10 kHz. At this time, the magnetic flux densities of the stator and the rotor serving as ferromagnetic bodies should not be saturated, and thus a maximum magnitude of the input current input to the excitation coil is 0.5 A. If a minimum number of turns of the excitation coil is determined to satisfy this condition, a minimum number of turns of the output coil is determined according to Equation 3. If an occupying ratio is calculated using the determined number of turns of the excitation coil and the output coil, the radii of the excitation coil and the output coil, and the area of the slot 112 between the tooth insulating units 121, it becomes a minimum occupying ratio, and this minimum occupying ratio is 3%. In other words, if the coil occupying ratio in the slot 112 becomes smaller than 3%, the input current input to the excitation coil increases and thus gives damage to a circuit which applies the input voltage, and also the magnetic flux density increases to distort a waveform of the output voltage, namely the induced voltage. In addition, the transformation ratio of the induced voltage generated at the output coil is lowered, thereby being vulnerable to external noise. Therefore, the coil occupying ratio per slot should be at least 3%.

The magnetic flux generated by the input current input to the excitation coil interlinks the output coil to generate an induced voltage. The normal magnetic flux generated by the input current is linked to the rotor. At this time, the magnetic flux generated by the input current is linked to the rotor to generate an eddy current, and the eddy current is generated in a direction opposite to the normal input magnetic flux. In addition, the magnetic flux components generated by the induced voltages generated at the first output coil and the second output coil collide with each other to give an influence to each other. As described above, the eddy current and the magnetic flux component generated by the induced voltage of the output coil distort the induced voltage of the output part to deteriorate the performance of the resolver. In order to minimize such distortion of the induced voltage at the output side, the coil occupying ratio per slot should be 35% or below.

In other words, the distortion of performance of the resolver may be reduced when the coil occupying ratio per slot is in the range of 3% to 35%.

Meanwhile, the magnetic flux may flow smoothly when a certain distance is maintained between the coil wound on a first tooth of two adjacent teeth 111 and a coil wound on a second tooth thereof. If the distance between the coil wound on the first tooth of two adjacent teeth 111 and the coil wound on the second tooth thereof is smaller, the magnetic fluxes respectively generated at the teeth 111 may interfere each other, which may cause distortion of an output waveform and thus generate an error in detecting a rotation angle. In order to reduce such an error, in the slot 112, a certain distance should be ensured between coils wound on two adjacent teeth 111, and a shortest distance between the coils should be 4 mm or above. FIG. 12 is a diagram showing a shortest distance (l_(min)) between the coils according to an embodiment of the present disclosure.

Hereinafter, results of the performance test of a resolver according to the coil occupying ratio per slot and the shortest distance between coils will be described with reference to Table 2 below.

Preparation of Samples

A stator 110 having twenty-four slots 112, insulation covers 120, a rotor 300 having eight salient poles and coils 140 are prepared. At this time, the stator 110 and the rotor 300 are ferromagnetic bodies with high magnetic permeability and are manufactured by laminating steel plates with a thickness of 0.5 mm in order to reduce a core loss. After the stator 110 and the insulation cover 120 are assembled, an excitation coil and an output coil are wound on each slot 112 by means of a circular winding machine to fabricate a resolver. Nine resolvers are prepared in total, and each resolver is fabricated to have an occupying ratio and a shortest distance between coils as in Table 2 below.

Measurement of an Error Rate

The test environment is identical to FIG. 7 described above. After each resolver is prepared as described above in relation to sample preparation, each resolver 630 is coupled to one end of a rotary shaft of a motor 610, and an encoder 620 is coupled to the other end of the rotary shaft. In addition, a calculator 640 analyzes output waveforms of the resolver 630 and the encoder 620. In detail, after the rotary shaft of the motor 610 is operated, the calculator 640 calculates a rotation angle profile by analyzing the output waveform of the resolver 630 and calculates an error rate by comparing the rotation angle profile with a rotation angle profile of the encoder 620. Each resolver 630 is tested ten times, among which a greatest error rate is defined as a maximum error rate. Generally, the resolver is demanded to have a maximum error rate of 0.5 or below. The coil occupying ratio is checked by means of x-ray inspection.

FIGS. 13, 14, 15, 16, 17, 18, 19, 20 and 21 are graphs showing an error rate of each resolver prepared as a sample, and each graph shows an error rate according to time in a test where a maximum error rate is found, when each resolver 630 is tested ten times. FIGS. 13, 14, 15, 16 and 17 are graphs respectively showing error rates of Examples 11 to 15 of Table 2, and FIGS. 18, 19, 20 and 21 are graphs respectively showing error rates of Comparative Examples 5 to 8 of Table 2.

Referring to FIG. 13, the resolver of Example 11 has a plus error rate with a maximum value of 0.3 and a minus error rate with a maximum value of −0.36. Therefore, the maximum error rate is 0.36 which is an absolute value of the minus error rate. Referring to FIG. 14, the resolver of Example 12 has a plus error rate with a maximum value of 0.32 and a minus error rate with a maximum value of −0.33. Therefore, the maximum error rate is 0.33 which is an absolute value of the minus error rate. Referring to FIG. 15, the resolver of Example 13 has a plus error rate with a maximum value of 0.29 and a minus error rate with a maximum value of −0.29. Therefore, the maximum error rate is 0.29. Referring to FIG. 16, the resolver of Example 14 has a plus error rate with a maximum value of 0.39 and a minus error rate with a maximum value of −0.42. Therefore, the maximum error rate is 0.42 which is an absolute value of the minus error rate. Referring to FIG. 17, the resolver of Example 15 has a plus error rate with a maximum value of 0.48 and a minus error rate with a maximum value of −0.44. Therefore, the maximum error rate is 0.48.

Referring to FIG. 18, the resolver of Comparative Example 5 has a plus error rate with a maximum value of 0.61 and a minus error rate with a maximum value of −0.12. Therefore, the maximum error rate is 0.61. Referring to FIG. 19, the resolver of Comparative Example 6 has a plus error rate with a maximum value of 0.24 and a minus error rate with a maximum value of −0.52. Therefore, the maximum error rate is 0.52 which is an absolute value of the minus error rate. Referring to FIG. 20, the resolver of Comparative Example 7 has a plus error rate with a maximum value of 0.64 and a minus error rate with a maximum value of −0.21. Therefore, the maximum error rate is 0.64. Referring to FIG. 21, the resolver of Comparative Example 8 has a plus error rate with a maximum value of 0.61 and a minus error rate with a maximum value of −0.23. Therefore, the maximum error rate is 0.61.

The above results are listed in Table 2 below.

TABLE 2 maximum occupying ratio shortest distance error rate Example 11 32 2.2 0.36 Example 12 32 3.7 0.33 Example 13 32 4.5 0.29 Example 14 37 4.5 0.42 Example 15 42 4.5 0.48 Comparative Example 5 37 2.2 0.61 Comparative Example 6 37 3.7 0.52 Comparative Example 7 42 2.2 0.64 Comparative Example 8 42 3.7 0.61

In Table 2, in Examples 11 and 12, it may be found that even though a shortest distance between coils in the slot 112 is less than 4 mm, if the coil occupying ratio is 35% or below, the maximum error rate is 0.5 or below, which satisfies product requirements. Meanwhile, in Comparative Examples 5 to 8, it may be found that if a shortest distance between coils in the slot 112 is less than 4 mm and the coil occupying ratio is greater than 35%, the maximum error rate is greater than 0.5, which does not satisfy product requirements.

In particular, if Examples 11 and 12 are compared with Example 13, a maximum error rate when the shortest distance between coils in the slot 112 is 4 mm or above and the coil occupying ratio is 35% or below is lower than a maximum error rate when the shortest distance between coils in the slot 112 is less than 4 mm and the occupying ratio is 35% or below. In other words, it may be found that the best performance is obtained when the shortest distance between coils in the slot 112 is 4 mm or above and the occupying ratio is 35% or below.

In Example 15, it may be found that even though the coil occupying ratio is greater than 35% in the slot 112, if the shortest distance between coils is 4 mm or above, the maximum error rate is 0.48 which is lower than 0.5 and thus satisfies product requirements. Meanwhile, in Comparative Examples 5 to 8, if the coil occupying ratio is greater than 35% in the slot 112 and the shortest distance between coils is less than 4 mm, the maximum error rate is greater than 0.5 and thus does not satisfy product requirements.

In other words, if any one of the condition that the shortest distance between coils in the slot 112 is 4 mm or above and the condition that the coil occupying ratio is 35% or below is satisfied, the resolver has a maximum error rate of 0.5 or below and thus satisfies product requirements. Moreover, if both conditions are satisfied, the maximum error rate is further lower than the case where only one of both conditions is satisfied, thereby ensuring better performance. Meanwhile, if both conditions are not satisfied, the maximum error rate is greater than 0.5 and thus does not satisfy product requirements.

While the present disclosure includes many features, such features should not be construed as limiting the scope of the present disclosure or the claims. Further, features described in respective embodiments of the present disclosure may be implemented in combination in a single embodiment. On the contrary, a variety of features described in a single embodiment of the present disclosure may be implemented in various embodiments, singly or in proper combination.

It should be understood by those skilled in the art that many adaptations, modifications and changes may be made to the present disclosure without departing from the technical aspects of the present disclosure, and the present disclosure described hereinabove is not limited by the disclosed embodiments and the accompanying drawings. 

1. A resolver, comprising: a stator made of a magnetic material and having a plurality of teeth and a plurality of slots alternately formed at an inner side thereof; insulation covers respectively having a tooth insulating unit formed at an inner side thereof corresponding to the teeth and mounted to the stator at both upper and lower surfaces of the stator; and coils wound on the teeth with the tooth insulating unit being interposed therebetween, wherein regarding winding widths of coils located at an outermost circumference among the wound coils, a ratio of a shortest winding width to a longest winding width is 0.69 or above and 1 or below.
 2. The resolver according to claim 1, wherein the ratio of the shortest winding width to the longest winding width among the wound coils is 0.8 or above and 1 or below.
 3. The resolver according to claim 1, wherein a coil occupying ratio per slot, which is defined by the following equation and represents a ratio of area occupied by the coils in a slot to which the insulation covers are fixed, is 35% or below: Coil occupying ratio per slot=(area occupied by coils in a single slot)/(area of a single slot).  Equation
 4. The resolver according to claim 3, wherein the coil occupying ratio per slot is 3% or above.
 5. The resolver according to claim 3, wherein in a slot to which the insulation covers are fixed, a shortest distance between coils wound on two teeth adjacent to each other is 4 mm or above.
 6. The resolver according to claim 3, further comprising: a rotor made of a magnetic material and configured to rotate based on a rotary shaft to change a gap permeance together with the stator. 7.-9. (canceled)
 10. The resolver according to claim 6, wherein the rotor is ring-shaped having a through hole formed at a center portion thereof so that the rotary shaft is inserted therein and a plurality of salient poles formed at an outer circumference thereof to change the gap permeance.
 11. The resolver according to claim 10, wherein the salient pole has an arc shape with a diameter smaller than at least a diameter of the rotor.
 12. The resolver according to claim 11, wherein a center of the arc is disposed spaced apart from a center of the rotor by a predetermined distance, and the arcs of the plurality of salient poles have the same diameter.
 13. A resolver, comprising: a stator made of a magnetic material and having a plurality of teeth and a plurality of slots alternately formed at an inner side thereof; insulation covers respectively having a tooth insulating unit formed at an inner side thereof corresponding to the teeth and mounted to the stator at both upper and lower surfaces of the stator; and coils wound on the teeth with the tooth insulating unit being interposed therebetween, wherein regarding winding widths of coils located at an outermost circumference among the wound coils, a ratio of a mean winding width of the coils located at the outermost circumference to a longest winding width is 0.83 or above and 1 or below, and wherein regarding the winding widths of the coils located at the outermost circumference among the wound coils, a ratio of the mean winding width of the coils located at the outermost circumference to a shortest winding width is 1 or above and 1.16 or below.
 14. The resolver according to claim 13, wherein regarding the winding widths of the coils located at the outermost circumference among the wound coils, a ratio of the shortest winding width to the longest winding width is 0.69 or above and 1 or below.
 15. The resolver according to claim 13, wherein regarding the winding widths of the coils located at the outermost circumference among the wound coils, a ratio of the mean winding width of the coils located at the outermost circumference to the longest winding width is 0.89 or above and 1 or below, and wherein regarding the winding widths of the coils located at the outermost circumference among the wound coils, a ratio of the mean winding width of the coils located at the outermost circumference to the shortest winding width is 1 or above and 1.1 or below.
 16. The resolver according to claim 15, wherein regarding the winding widths of the coils located at the outermost circumference among the wound coils, a ratio of the shortest winding width to the longest winding width is 0.8 or above and 1 or below.
 17. The resolver according to claim 13, wherein a coil occupying ratio per slot, which is defined by the following equation and represents a ratio of area occupied by the coils in a slot to which the insulation covers are fixed, is 35% or below: Coil occupying ratio per slot=(area occupied by coils in a single slot)/(area of a single slot).  Equation
 18. The resolver according to claim 17, wherein the coil occupying ratio per slot is 3% or above.
 19. The resolver according to claim 17, wherein in a slot to which the insulation covers are fixed, a shortest distance between coils wound on two teeth adjacent to each other is 4 mm or above.
 20. The resolver according to claim 17, further comprising: a rotor made of a magnetic material and configured to rotate based on a rotary shaft to change a gap permeance together with the stator. 21.-23. (canceled)
 24. The resolver according to claim 20, wherein the rotor is ring-shaped having a through hole formed at a center portion thereof so that the rotary shaft is inserted therein and a plurality of salient poles formed at an outer circumference thereof to change the gap permeance.
 25. The resolver according to claim 24, wherein the salient pole has an arc shape with a diameter smaller than at least a diameter of the rotor.
 26. The resolver according to claim 25, wherein a center of the arc is disposed spaced apart from a center of the rotor by a predetermined distance, and the arcs of the plurality of salient poles have the same diameter. 